This invention relates to a capacitive activated transducer, and more particularly to a transducer sensitive to human touch for generating a change in frequency of an oscillator output.
Automatic data processing systems of the computer controller type, and in particular data word processing systems, require directive and corrective instructions from an operator to achieve efficient and satisfactory operation. With such systems, it is important to reduce operator reaction time to a minimum which makes necessary a communication link between the operator and the system, and vice versa, that is simple and reliable. Further, any system for presenting information to and receiving instructions from an operator should be rapid and easily interpreted.
Recently, there has been a general acceptance of a technique utilizing a means for displaying data for rapid and easy communication to an operator and, of course, this is usually provided by the cathode ray tube (CRT), which may be controlled to display data on a screen. Such data is often presented in a line format comprising numerical and alphabetic characters and other symbols, and the items of information, comprising individual symbols or combination of symbols, appear on the screen of the cathode ray tube in much the same manner as presented on a page of typed script. Thus, the cathode ray tube provides a convenient and satisfactory communication link between the data processing system and the operator.
The communication link is not so satisfactory between an operator and the system, particularly in the case of accepting instructions from the operator. The operator may need to perform a processing function with respect to any of the data displayed on the CRT screen. For example, a particular character or set of characters may require deletion and substitution with other characters. Also, one entire area of the display may need to be rearranged with other data in the system. To perform this function it is necessary to make available to the operator a communication link that enables identification of the character or characters in terms of its location on the screen of the cathode ray tube.
Heretofore, there have been many efforts made to enable an operator of a data processing system to identify a particular character or area of characters displayed on the screen of a cathode ray tube. In one such prior art system, a so-called touch wire overlay mask is mounted upon the screen of the cathode ray tube and connected to suitable response devices that enables the item identification function to be performed by the operator applying a finger touch to the appropriate region of the mask. The response devices connected to the touch wire overlay mask require extensive and complex circuitry, but most important have not been as reliable as desired. Other attempts to establish a communication link between an operator and a data display have utilized light grids in an attempt to locate where an operator's finger is placed by interrupting the circuit of a photosensitive device. Still another approach found in the prior art to solve the problem of operator communication utilizes one or more capacitors which are integrally associated with the screen of the cathode ray tube and are intentionally of a high leakage character. When the leakage field is interrupted by an operator's finger touch, the capacitive reactance is changed and a bridge circuit balance is upset.